Function Description of Major Items

The following areas were considered and emphasized when designing the system:

• Sample cooler

The sample cooler, manufactured by SENTRY, is a shell and tube heat exchanger. The shell design pressure is 31 barG and the tube design pressure is 300 barG. The cooler is used to cool the condensate sample to 25ºC using the closed cooling water (a demineralisation cooling water system). The condensate temperature is usually 30 to 35ºC. The best temperature for conductivity and pH measurement is 25ºC, although the latest analysers have an automatic temperature compensation function.

V21 to regulate the sample temperature after the cooler. The closed cooling water flow rate does not need to be adjusted regularly because the condensate temperature is quite stable. The closed cooling water flow rate is displayed by the flow indicator F7. Valve V23 is a pressure relief valve, set at 6 barG. If the cooling water pressure exceeds 6 barG the valve will open.

Figure 5.10 Closed cooling water loop P&ID

•Condensate sample loop

Figures 5.11 and 5.12 show the condensate sample loop components. When the system is put into service, blowdown valve V1 is used to flush the condensate sample line ahead of the cooler until the sample is clean. V1 remains shut during the normal operation. Isolation valve V2 is used to isolate the sample and is open during normal operation.

Figure 5.12 Condensate sample loop

Non-return valve V3 is used to prevent the condensate sample or air being sucked back into the condenser hotwell that is under a vacuum. This would only happen if there was not enough flow through the recirculation line. Component E1 is the cooler. Pressure-reducing valve V4 is used to reduce the sample pressure from 19 barG to 2 barG which is the nominal pressure for the analyser sensors. The sample pressure after the cooler is displayed on pressure gauge P1. Valve V8 is used to take a manual sample from the wet analysis rack. In addition, V8 can also be used to flush the sample line before the analysers when the system is put into service.

• High pressure protection

The adjustable backpressure regulator V6 is used to stabilise the analyser inlet pressure. As shown in Figure 5.11, if the sample pressure exceeds 2 barG (current setpoint) the regulator V6 opens to divert the excess sample to the drain. The higher the pressure, the more the regulator opens.

• High temperature protection

Thermal Shutoff Valve (TSV) V5, manufactured by SENTRY, is installed

V1 V4 V2 V3 V5 T1 P1 E1 V8 V6 V7

The sensor/actuator is directly exposed to the sample. If the sample temperature after the cooler exceeds 49ºC, the TSV will automatically shut to isolate the sample and protect the analyser sensors the from high temperature damage.

The TSV can be reopened manually after a trip by pushing the button on top of the TSV. Once the TSV is closed, the pressure in the sample line will rise, and if the pressure exceeds 2 barG, the back pressure regulator V6 will open to maintain the pressure at 2 barG by diverting the sample to drain.

As shown in Figure 5.12, the TSV(V5) also has a switch at the bottom to provide a signal for a remote alarm. This switch is wired through the electrical distribution box on the rack from where the signal is routed to the DCS. The signal is configured to be fail-safe because it is a critical signal. Once the alarm goes off, the operator needs check the valve locally. The valve will remain closed after it trips, and can only be opened again by pushing the reset button after the sample temperature falls below 49ºC.

•Low flow detection

Every analyser in the system must have an adequate sample continuously flowing through the analytical sensor in order to guarantee that the data sent to the DCS is accurate. Each analyser is therefore equipped with a sample flowmeter and low flow ring sensor as shown in Figure 5.13. The flowmeter ring sensor with a bistable switching action de-energies the relay in the amplifier installed in the electrical distribution box when the float falls to the trigger level. The relay remains de-energised, even if the float drops below the sensor. The relay re-energises as soon as the float crosses the trigger level in the upward direction and moves into the normal operating range.

Figure 5.13 Flow meter and low flow sensor

The condensate sample flows upwards through the flowmeter. The position of the ball float indicates the sample flow rate. The sample flow can be adjusted using the knob at the top of the meter. The sample flow rate is usually kept between 150 and 200 ml/min. The trigger level of the ring sensor is 100ml/min. If the sample flow rate falls below 100 ml/min, the ball float will reach the ring sensor, de-energising the relay and generating a low sample flow alarm in the DCS.

Six low sample flow switches are connected in series and share one common alarm in the DCS. The operator must check and adjust the sample flow locally because the common alarm does not indicate which analyser has a low flow. The alarm resets only when all analysers have an adequate sample flow rate.

• Dual cation resin columns

The cation conductivity is measured after the condensate sample has passed through a column of cation exchange resin in the hydrogen form. The effect of this

F1 F2

Low Flow Sensor Adjustable Knob

The existing conductivity analysers only have one cation exchange column as shown in Figure 5.14. The cation exchange resin in the column needs to be changed every three or four days when the resin is exhausted. The measured cation conductivity is very high immediately after the resin has been changed and the new resin usually take approximately one hour to rinse down. The operator has to simulate the output value of the analyser before changing the resin to avoid generating a high cation conductivity alarm in the DCS, then remove the simulation once the measured value settles back down to normal.

Figure 5.14 Existing single cation resin column

The new condensate monitoring system uses a dual resin column configuration as shown in Figure 5.15. Valves V9 and V10 are the inlet isolation valves for each column. The three-way valve V11 is used to switch over between the two columns. One column is in service at a time. The position of the V11 shown in Figure 5.15 indicates that the left-hand column (C1) is in service.

The condensate sample flows downward through the resin column after passing through the specific conductivity sensor SC1. The sample then enters the cation conductivity sensor CC1. The re-generated resin and exhausted resin can be distinguished by colour. The re-generated resin is brown and exhausted resin is dark red.

Figure 5.15 Dual cation exchange resin column diagram

The columns are easily switched over. For example, as shown in Figure 5.15, if the resin in the right-hand column (C2) is exhausted, the column can be switched over simply by changing the position of three-way valve V11. It is not necessary to operate Valves V9 and V10, and they can be left open when removing the columns for the purpose of replacing the resin because the quick-release fittings are self sealing. The exhausted resin column is easily removed by pulling the quick-release coupling at the both ends of the column. The resin column is easily reconnected after refilling with re-generated cation exchange resin.

Based on commissioning experience, re-generated resin usually takes 10 minutes to rinse down, which is much faster than the existing Siemens resin column. In

V9 V10 V11 SC1 CC1 C1 C2 Quick-Release fitting